Polymers with pendant alkyne groups

While a large majority of the photoerosslinkable polymers that were investigated over the years erosslink by free-radieal meehanism, utilization of ionie meehanism has reeeived some attention. This ineludes polymers with pendant eyelie ethers and alkyne groups. 

Figure 12.8 Schematic representation of (a) step-growth coupling of bivalent azide and bivalent acetylene telechelic polymers (b) polymer modi cation by CuAAC of pendant alkyne groups of polymers, e.g., poly(vinyl acetylene), with an azide-bearing substrate and (c) functionalization of polymer by CuAAC of pendant azide with alkyne-bearing functional moiety. Azide terminated dendrimers are similarly subjected to CuAAC with alkyne-derivatized functional moieties to achieve desired functionalization of dendritic macromolecules.

SCHEME 8.4 Schematic illustration of the processes involved in the graft copolymerization of DMAEMA from PVDF main chains via AGET-ATRP, preparation of PVDF-g-PDMAEMA membrane by phase inversion, and quaternization of PVDF-g-PDMAEMA membrane by propargyl bromide to produce PVDF-g-PQDMAEMA membrane with pendant aUcyne groups, covalent immobilization of hyperbranched polymer HPG-Nj or PEI-Nj onto the PVDF-g-PQDMAEMA membrane surface via surface alkyne-azide click reaction. PVDF, poly(vinylidene fluoride) DMAEMA, 2-(V, V-dimethylamino)ethyl methacrylate VC = L-ascorbic acid PMDETA = V,V,M,V, A"-pentamethyl diethylene triamine HPG-N3 = az/hyperbranched polyglycerols PEI-N3 = azirfo-polyethylenimine. Reprinted with permission from Reference 114. Copyright 2013 American Chemical Society. 

Employing a molar excess of the alkyne over the active hydrogen of only 12 percent the selectivity (determined by proton NMR after work-up) may be expressed as the ratio of Si-C=CH- to Si-CH2-CH2-CO-, which is about 100 1 [16]. The same reaction, carried out with silicone polymers with 10 or more pendant silicon-bonded hydrogen atoms, proceeds similarly cleanly without noticeable crosslinking by acrylic hydrosilylation. A slight excess of triple bond over Si-H groups is mandatory to suppress this side reaction as well as hydrosilylation of the olefinic group of the 2-silylalkene isomer product (see Table 2.). 

Another example of self-assembly of porphyrin-containing polymer was illustrated by Li et al.73 Polyacetylene functionalized with fullerene and zinc porphyrin pendant groups were synthesized by polymerizing the corresponding fullerene/porphyrin substituted alkyne monomers with rhodium(I) norbomadiene catalyst (Scheme 5.5).74 Polymers with different ratio of C60 and porphyrin were synthesized. The polymers showed photocurrent response when the thin films were irradiated with white light, which was due to the electron transfer from the photo-excited porphyrin to the C60 units. In addition, the copolymers aggregated into ellipse-shaped nanorod structures with a diameter of approximately 100 nm and a length of... 

A copolymer bearing proline and permethylated p-CD was used as catalyst in aldol condensation [23]. The linear copolymer bearing both pendant permethylated p-CD and proline groups was designed on the basis that the hydrophobic cavity of the CDs could approach the substrates close to the proline that acted as catalyst through host-guest interactions. The synthesis of the CD monomer was carried out by a copper-catalyzed azide-alkyne cycloaddition. The CD monomer was then polymerized with a protected hydroxyproline methacrylate to give the linear polymer with a monomer ratio proline/CD of 4.The Me-p-CD-Pro polymer was subsequently obtained after acid deprotection of proline (Scheme 2.9). 

Tunca et al. [27, 28,38] reported in a series of papers on a multi-click approach for the preparation of brush copolymers. The backbone consisted of homopolymers, statistical polymers, or block copolymers from ONBEs with orthogonal side groups for Diels-Alder click reaction [27,28,38], azide/alkyne click reaction, [27, 28, 38] and nitroxide coupling [27]. In a grafting-to approach, maleimide-or ONBE-functionalized polymers (PEG, P BA, PMMA (56)) were attached by Diels-Alder click reaction with the anthracene groups pendant at the polymer backbone (55) (Scheme 9.8b). PCL chains were attached by an azide/alkyne click reaction, while a combination of Diels-Alder and azide/alkyne click reaction allowed the synthesis of graft copolymers with PS-/ -PEG-, PS-h-PMMA-, or PS-/ -P BA side chains. 

Other functional groups that can be used to form photocrosslinkable polymers are alkyne, male-imides, stilbene, styrene, 1,2,3-thiadiazole, thymine, and anthracene. Pendant groups with anthracene moiety, however, are believed to crosslink by a 47t + An type of cycloaddition ... 

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